I'll be uploading my own instance of this bug tonight. I don't know if this is reported in this (or other) threads, but when the Turn button disappeared for me I also couldn't move the view. If I clicked and dragged, the view would shift a small amount and then snap back to where it was.
My save is from a few turns before the bug manifests, which gave me some options to try and get around it. For me, the bug seems to be related to trying to rush buy a ship to protect a planet from an incoming Troop ship. When I tried to buy a defender, the Arceans arrived before it was complete and invaded (and lost, 2B v 12B) and then the Turn button would be gone. If I didn't try to buy the ship, then the Turn button was fine.
This was on a medium sized map.